1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method using laser light illumination which method is superior in mass-productivity and can provide small variations and a high yield, and to a laser processing apparatus usable in such a method. In particular, the invention relates to a method and an apparatus for improving or recovering the crystallinity of a semiconductor material part or all of which is made of an amorphous component, a substantially intrinsic polycrystalline semiconductor material, or a semiconductor material which crystallinity has been greatly degraded due to irradiation of ions, ion implantation, ion doping, or the like, by illuminating such a semiconductor material with laser light.
2. Description of the Prior Art
In recent years, extensive studies have been made to lower the temperature of semiconductor manufacturing processes. This is due to the need of forming semiconductor devices on an insulative substrate, such as a glass substrate, that is not highly heat resistant, as well as to miniaturization and multi-layering of devices.
In semiconductor processes, it is sometimes necessary to crystallize an amorphous component included in a semiconductor material or an amorphous semiconductor material, cause a semiconductor material to restore its crystallinity that has been degraded due to irradiation with ions, or improve the crystallinity of a crystalline semiconductor material.
Conventionally, thermal annealing is used for such purposes. When silicon is used as a semiconductor material, crystallization of an amorphous material, recovering and improvement of the crystallinity, and the like are performed by annealing of 0.1 to 48 hours or longer at 600 to 1,100° C.
In general, as the temperature is increased, the thermal annealing can be performed in a shorter period and becomes more effective. At a temperature lower than 500° C., the thermal annealing causes almost no effects. Therefore, from the viewpoint of lowering the process temperature, it is necessary to replace a conventional manufacturing step involving thermal annealing with a step using some other means.
An annealing technique using laser light illumination now attracts much attention as an ultimate low-temperature process to replace the thermal annealing. This is because laser light can be applied only to a portion that requires high energy equivalent to that of the thermal annealing and, therefore, it is not necessary to expose the entire substrate to a high-temperature environment.
Generally, there have been proposed two methods of laser light illumination. In the first method, a CW laser such as an argon ion laser is used to apply a spot-like beam to a semiconductor material. After being melted, the semiconductor material is gradually solidified and thereby crystallized due to an uneven energy profile of the beam and movement of the beam.
In the second method, a pulsed laser such as an excimer laser is used to apply a high-energy laser pulse to a semiconductor material. The semiconductor material is crystallized by instantaneously melting and then solidifying it.